1. Field of the Invention
This invention relates to external medical instruments that are in physical contact with a patient""s body to communicate with or test the function of implantable medical devices (IMDs) implanted in the patient""s body or to provide a therapy or to measure a physiologic condition of the patient""s body and capable of communicating with other medical instruments or systems located at a distance from the patient, and particularly to safety systems for protecting the patient from harm due to electrical potentials.
2. Description of the Prior Art
In the field of programmable IMDs, it has become common to provide an interactive, transceiver system for both remotely programming operating functions, modes and parameters of the implanted device, and for telemetering out data related thereto on command by RF telemetry to an external medical device, commonly denoted a xe2x80x9cprogrammerxe2x80x9d. Such IMDs include cardiac pacemakers, cardiac and other physiologic monitors, implantable drug dispensers, nerve, muscle, and brain stimulators of various types, cochlear implants, blood pumps, cardiomyostimulators, and tachyarrhythmia-control devices, e.g., implantable cardioverter/defibrillators (ICDs) for delivery of staged therapies to the ventricles and/or the atria, etc., to treat tachyarhythmias.
At the present time, both analog and digital information or data is typically transmitted by uplink RF telemetry from such IMDs to the external programmer upon receipt of a downlink telemetry interrogation command from the external programmer. The analog information has typically included battery voltage, physiologic signal amplitudes sensed in real time from sensors or sense electrodes, e.g., sampled cardiac electrocardiogram or EGM amplitude values, and, in the case of implanted pacemaker and ICD IPGs, pacing pulse and/or cardioversion shock amplitude, energy, and pulse width and lead impedance. Digital information includes digitized operating data, e.g., markers signifying device operations and data typically stored in RAM or ROM and transmitted in response to an interrogation command from such IMDs. Such stored data includes historic statistics related to device performance, episodic physiologic data stored in response to detection of an episode of interest or delivery of a therapy, e.g., cardiac electrogram (EGM) segments, current programmed operating modes and parameter values, implant data, and patient and IMD identifier codes. Uplink telemetry is therefore employed to interrogate the IMD functions and memory and to confirm re-programming of operating modes and parameter values programmed in a downlink telemetry transmission.
Since the time that such telemetry systems first became available, IMDs have proliferated in types and successive models or generations of each type that have been steadily improved in longevity and designed with increased programmable functions and capabilities. At first, in some instances, a single external programmer was designed to function with a single type or family of IMDs that could not be used to program or interrogate other IMD types or families or new generations thereof. A new programmer would have to be provided to the physicians as successive programmable IMD models and IMD functions became clinically available. In some instances, this problem was perceived and dealt with by providing the capability of upgrading the programmer so that it could communicate with the newly available IMDs and at least confirm the identity of the IMD during a programming session for safety and record keeping reasons before proceeding to the programming and interrogation functions.
Medtronic, Inc. and other manufacturers developed microprocessor-based programmers that operated using software routines provided by dedicated, plug-in ROM modules or cartridges to enable the operation of the programming and interrogation telemetry with regard to specific model or series of models of IMDs. In such systems, the programmer is incapable of communicating with a given IMD model unless the appropriate plug-in module or cartridge is first installed. For example, for many years, particular Medtronic(copyright) MemoryMod(copyright) ROM cartridges were developed and supplied to enable the physician to upgrade the programmer to program and interrogate a specific set of new generation Medtronic(copyright) pacemaker implantable pulse generator models.
More sophisticated, computer based programmers have been developed that also can be upgraded, including, for example, the Medtronic(copyright) Model 9710 and 9760 programmers and the more recent Medtronic(copyright) Model 9766 and 9790 programmers which employ the Medtronic(copyright) Model 9765 programming head. It is possible to load updated software for programming new generation IMDs onto a hard disk drive from floppy disks or compact discs or through a modem and many of the other alternative ways that programs are added to personal computers, for example.
Telemetry sessions between an IMD and the external programmer are typically initiated and conducted in the manner described in commonly assigned, U.S. Pat. Nos. 5,168,871 and 5,683,432. Current telemetry systems are designed to provide two-way telemetry by RF signal transmission and linkage between an antenna coil contained in the IMD canister and an antenna coil or coils contained in the programming head of the external programmer. Typically, the programming head is placed against the patient""s skin overlying the IMD, and a communications link is established as depicted and described in the above-referenced ""871 patent by closure of a reed switch within the IMD by the magnetic field of a permanent magnet incorporated into the programming head. Uplink telemetry of analog and digital data of the IMD and downlink telemetry of programming and interrogation commands to the IMD is conducted in a telemetry session according to a telemetry format that is related to the particular IMD.
Programmers and IMDs have also been disclosed that transmit and receive programming instructions and data at high frequencies employing very small antennae and that eliminate the need for the closure of the reed switch by the external magnet during programming.
FIG. 1 is a simplified view of the typical bidirectional telemetry communication between a prior art external programmer 26 and an IMD comprising a cardiac pacemaker implantable pulse generator (IPG) 12 and an associated lead 14, for example, employing the programming head 20. The IPG 12 is implanted in the patient 10 beneath the patient""s skin and typically oriented to the skin surface as is typical in the implantation of any programmable and interrogatable IMD. The IPG 12 is electrically coupled to the heart 18 of the patient 10 through pace/sense electrodes and lead conductor(s) of at least one cardiac pacing lead 14 in a manner known in the art. The IPG 12 contains an operating system that may employ a microcomputer or a digital state machine for timing sensing and pacing functions in accordance with a programmed operating mode. The IPG 12 also contains sense amplifiers for detecting cardiac signals, patient activity sensors or other physiologic sensors for sensing the need for cardiac output, and pulse generating output circuits for delivering pacing pulses under control of the operating system in a manner well known in the prior art. The operating system includes memory registers or RAM for storing a variety of programmed-in operating mode and parameter values that are used by the operating system. The memory registers or RAM may also be used for storing data compiled from sensed cardiac activity and/or relating to operating history for telemetry out on receipt of a retrieval or interrogation instruction. All of these functions and operations are well known in the art, and many are employed in other programmable, IMDs to store operating commands and data for controlling device operation and for later retrieval to diagnose device function or patient condition.
Programming commands or data are transmitted between an IPG telemetry antenna within IPG 12 and a programming head telemetry antenna within programming head 20 during a telemetry uplink transmission 28 or downlink transmission 30. In a telemetry uplink transmission 28, the programming head telemetry antenna operates as a telemetry receiver antenna, and the IPG telemetry antenna operates as a telemetry transmitter antenna. Conversely, in a telemetry downlink transmission 30, the programming head telemetry antenna operates as a telemetry transmitter antenna, and the IPG telemetry antenna operates as a telemetry receiver antenna.
INTERROGATE push-button 23 and PROGRAM push-button 25 and an LED display 22 are provided on the programming head 20 and are also electrically connected through electrical cable 24 to external programmer 26. The INTERROGATE and PROGRAM push-buttons 23 and 25 are provided to be selectively depressed by the medical care giver to start the telemetry uplink and downlink transmissions 28 and 30, respectively, as described in detail in the above-referenced ""871 patent. The LED display 22 is also provided that is coupled to a sense circuit in programmer 26 described above and is illuminated during a telemetry uplink or downlink transmission 28 or 30 to alert the medical person that the transmission is taking place.
An ECG cable 60 is also provided extending from programmer 56 having a plurality of ECG skin electrodes that can be placed at specified points of the patient""s torso and limbs. Graphics display screen 55 is used to display the patient related data and menu choices and data entry fields used during telemetry uplink and downlink transmissions 28 and 30. The user interacts with programmer 26 by touching stylus 56 against a selected location on screen 55 that displays the appropriate menu choices. Other components within the programmer console are described below with reference to FIG. 2.
The programmer 26 is typically employed during implantation of the IMD to program initial operating modes and parameter values and to obtain implant patient data for the patient""s medical record. The programmer 26 is also employed from time to time during routine patient follow-up visits or when a clinical issue arises causing the patient to seek medical assistance in order to uplink telemeter patient data and IMD operating stored data to the programmer for analysis. In use, the attending medical care giver applies the ECG skin electrodes to the patient""s body and/or holds programming head 20 against the patient""s skin and over the IPG 12 to align the transceiver antennas in each as close together and as still as possible to ensure reliable telemetry transmission during the time that it takes to complete a telemetry uplink or downlink transmission 28 or 30.
A simplified block diagram of an exemplary prior art programmer 26 is set forth in FIG. 2 and is based upon the above-referenced Medtronic(copyright) Model 9760 programmer or preferably the Model 9790 programmer that is depicted and described in the above-referenced ""432 patent. Programmer 26 is a personal computer type, microprocessor-based device incorporating a central processing unit 50, which may be, for example, an Intel 80386 or 80486 or Pentium microprocessor or the like. A system bus 51 interconnects CPU 50 with a hard disk drive 52 storing operational programs and data and with a graphics circuit 53 and an interface controller module 54. A floppy disk drive 36 (or a CD ROM drive) is also coupled to bus 51 and is accessible via a disk insertion slot (not shown) within the housing of the programmer 26. Programmer 26 further comprises an interface module 57, which includes digital circuit 58, non-isolated analog circuit 59, and isolated analog circuit 40. Digital circuit 58 enables interface module 57 to communicate with interface controller module 54.
An alphanumeric keyboard 45 for entering text or numbers and other symbols is optionally provided to allow the medical person to communicate with CPU 50 in the programmer 26. However, the primary user communication mode is through graphics display screen 55 of the well known xe2x80x9ctouch sensitivexe2x80x9d type controlled by graphics circuit 53 and a stylus 56 coupled thereto. As noted above, graphics display screen 55 is used to display the patient related data and menu choices and data entry fields used during telemetry uplink and downlink transmissions 28 and 30, and stylus 56 is used to select appropriate menu choices.
Graphics display 55 also displays a variety of screens of telemetered out data or real time data. Programmer 26 is also provided with a strip chart printer 63 or the like coupled to interface controller module 54 so that a hard copy of a patient""s ECG, atrial and/or ventricular electrogram (AEGM, VEGM), Marker Channel or of graphics displayed on the display 55 can be generated.
The transceiver circuitry 41 is connected to the interface module 57 of the external programmer 26 via conductors in an elongated electrical cable 24. During a telemetry uplink transmission 30, the telemetry receiver circuit in transceiver 41 is enabled. The telemetered out RF pulses of the uplink transmission 30 are detected, demodulated, decoded and applied to the digital circuit 58 to be digitized and recorded in RAM or in a hard or floppy disk or the like. The digitized data may be contemporaneously or later retrieved from memory and displayed on graphics display screen 55 or printed out for the attending medical personnel.
The analog and ventricular channel EGM signals from atrial and ventricular pace/sense electrodes may be digitized within IPG 12 and uplink telemetered to programmer 26 on receipt of a suitable INTERROGATE command. The uplink transmission 28 of the telemetered EGM signals are received in programming head 20 and provided to non-isolated analog circuit 59. Non-isolated analog circuit 59, in turn, convert the digitized EGM signals to analog EGM signals (as with a digital-to-analog converter, for example) and presents these signals on output lines designated in FIG. 2 as AEGM OUT and VEGM OUT. These output lines may then be applied to a separate strip-chart recorder or the like to provide a hard-copy printout of the AEGM or VEGM signals transmitted from IPG 12 for viewing by the physician
The IPG 12 may also be capable of generating so-called marker codes indicative of different cardiac events that it detects. An IPG with Marker Channel capability is described, for example, in commonly assigned U.S. Pat. No. 4,374,382, incorporated by reference herein in its entirety. The markers provided by IPG 12 may be received by programming head 20 and presented on the MARKER CHANNEL output line from non-isolated analog circuit 59.
To initiate a telemetry uplink transmission 28, the telemetry transmitter in transceiver 41 is enabled in response to depression of the INTERROGATE push-button to generate an INTERROGATE RF pulse command that first initiates a downlink telemetry transmission 30 of a series of RF pulses. Each RF pulse of the instruction or command that is transmitted causes the IPG L-C tuned circuit to ring. The train of induced voltages is detected and decoded by the receiver circuit in the IPG transceiver. After the command or instruction is decoded, the stored data to be uplink transmitted is encoded into PPM modulated RF pulses in data frames. Methods and apparatus for formatting such uplink data frames for Medtronic(copyright) IPGs and other IMDs are set forth in detail in the above-referenced ""404 patent. The transmitter circuit in the IPG transceiver applies voltage to the IPG RF antenna causing the L-C tuned circuit to ring and generate the uplink RF pulses which induce signals in the programming head telemetry antenna. The induced signals are detected in the telemetry receiver circuit in transceiver 41 and applied as a pulse train on cable 24 to interface module 57 where the frame of a series of such signals is decoded so that the data can be recorded or displayed as described above.
Some preliminary electrical tests are typically performed after an implantable cardioversion or defibrillation lead is implanted and before the lead is finally attached to the IMD IPG. For example, if the lead is a pacing lead that is to be connected to an implantable pacemaker IPG or ICD IPG, the lead is first implanted (e.g., transvenously) so that the distal electrode(s) is in electrical contact with cardiac tissue as shown in FIG. 1. Then, the proximal lead connector remaining outside the skin is temporarily connected to an appropriate external stimulator typically through an elongated surgical cable so that stimulation thresholds effective to capture the heart, sensing thresholds, and lead impedance data can be collected. The external instrument is referred to as a pacing system analyzer (PSA) when a pacing leads are tested or as a defibrillation system analyzer (DSA) when cardioversion/defibrillation leads are also tested as described in U.S. Pat. No. 5,679,022. Exemplary PSAs include the MEDTRONIC(copyright) Model No. 5311B PSA, the MEDTRONIC(copyright) Model 5410/S reusable surgical cable and the combination of the MEDTRONIC(copyright) Model 5411/S reusable adaptor and Model 5455/S disposable surgical cable. Such PSA models are stand-alone battery powered devices having integral operating controls and display.
A DSA is used to apply an appropriate signal (usually a low amplitude AC signal) to the shocking electrodes in order to induce fibrillation. Shocking pulses of varying energies are then applied to the cardiac tissue across the shocking electrodes in order to ascertain the defibrillation threshold, i.e., the amount of energy required in a defibrillation shock pulse in order to defibrillate the heart. The determined defibrillation threshold is then used to guide the initial setting of the defibrillation energy generated by the ICD IPG.
In use of a PSA, a series of stimulation pulses of varying energies, or other test signals (such as signals to measure the lead impedance) can be applied to the cardiac tissue through the lead in order to ascertain the capture threshold at which the cardiac muscle tissue contracts, or in order to determine other parameters associated with the lead. The results of such capture threshold testing, or other testing, advantageously provide an indication as to whether the distal electrode is making good contact with the cardiac tissue, as well as what the initial setting of the pacing pulse energy should be to reliably capture the heart.
FIG. 1 also illustrates a PSA 70 having a PSA cable 72 extending to connectors 74 and 76 adapted to be coupled to the proximal connector elements of a bipolar lead 14, for example, that would exit the skin incision that the lead 14 is introduced through prior to attachment to the IPG 12 and the subcutaneous implantation of IPG 12. In this particular instance, the PSA 70 is the MEDTRONIC(copyright) Model No. 8090 PSA that is built into a lid of a compartment of the Model 9790 programmer 26. Software to operate the Model 8090 PSA pulse generators, sense amplifiers and impedance measurement circuitry, to display menus for selection, the delivered pacing pulses and the test values and to print a record of the same is loaded into the programmer operating system.
In use, the clinician enters control values and commands for operating the Model 8090 PSA using the keyboard 45 and display 55. The Model 8090 PSA executes the commands under the control of the CPU 50 to deliver an impedance test pulse, for example, to measure voltage and current and to derive an impedance value. The derived value or other signal is then displayed on display 55, printed out by printer 43 and stored in memory with other patient data.
There is a risk of accidental injury to a patient whenever electrically powered medical equipment is coupled with the patient""s body, and steps have been taken to minimize that risk using a conventional programmer 26 or PSA 70 or other ECG equipment. In FIG. 2, the programmer 26 includes a medical grade power supply 66 that powers the CPU 50, the other circuitry and the peripheral devices including the display 55 and printer 43 and is typically coupled to electrical mains. The power supply 66 is electrically isolated from the powered circuitry and components through a high voltage isolation transformer to prevent any mains current or voltage from being coupled to the ECG leads 60 or through the PSA 70 and the cable 72 to the implanted leads, e.g., lead 14.
In addition, an isolated analog circuit 40 in interface module 57 is provided to receive the external ECG signals via ECG cable 60 and electrophysiologic (EP) stimulation pulse signals. In particular, analog circuit 40 receives ECG signals from patient skin electrodes of ECG cable 60 (FIG. 1) and processes these signals before providing them to the remainder of the programmer system in a manner well known in the art. Isolated analog circuit 40 further operates to receive the EP stimulation pulses from an external EP stimulator for the purposes of non-invasive EP studies, as is also known in the art. Similarly, the PSA 70 includes an optical isolator. Typically, high voltage withstanding, optical isolators or opto-isolators of the types described in commonly assigned U.S. Pat. No. 5,448,997 (block 22) or as described in U.S. Pat. No. 4,742,831 provide this electrical isolation.
The permanent coupling of a PSA, e.g., PSA 70, with the programmer reduces its flexibility of use. There may be instances when the PSA is advantageously used simply as a temporary external pacemaker wherein the programmer 26 is superfluous to that function or presents an unnecessary risk. For example, stray voltages may be accidentally introduced into the programmer 26 and conducted to the PSA 70.
It is also desirable to enable communications between the system at the site where the patient is located and with more remote equipment within the same building or elsewhere at remote locations. There are references to inclusion of modems in various types of external instruments as set forth in U.S. Pat. Nos. 4,751,726, 5,425,373, 5,758,652, and 5,725,559, and in commonly assigned U.S. Pat. Nos. 4,593,284, 4,987,897, and 5,836,989. However, a programmer resident modem coupled to telephone lines presents serious electrical hazards to a patient coupled to the same programmer by ECG cables or PSA or DSA cables. Surge voltages can be transmitted over telephone lines that bear the risk of being conducted to the patient and causing fibrillation or other malignant tachyarrhythmia of the heart.
In addition, the operating speeds and characteristics of modems continue to evolve. Moreover the various ways of interconnecting with the Internet, various LANs and intranet systems and the characteristics of those systems continue to evolve. Furthermore, national and regional telecommunication systems and standards and regulations both vary and continue to change and evolve at differing rates. For all of these reasons, any given modem incorporated into a programmer can become obsolete or not possible to meet all conditions and standards encountered throughout the world.
Thus, the system including a programmer, IMD and PSA (or PDA) described above with reference to FIGS. 1 and 2 and including a built-in modem is deficient in a number of respects. It is desirable to increase the capabilities of the programmer and the IMD to increase the operating modes and parameters and increase the available therapy delivery options and monitoring capacity of the IMD. The types of permanent and temporary IMDs continue to evolve, and more than one IMD may be implanted in or carried by a given patient. In some cases, it may be desirable to obtain physiologic data and IMD data from more than one such IMD employing the same programmer or external instrument to gather, correlate and display, store print or transmit such data at the same time.
But, it is desirable to miniaturize and lighten the programmer and any other associated equipment as described. As the size of the programmer is reduced, it becomes more difficult to fit such additional components and features into it and to provide an adequate power supply for them.
Consequently, a need remains for further improvements in interface devices for programmers and other external equipment including communications lines that allow the size of the programmer to be minimized, that increase operating capabilities, and that minimize the risk that the patient will be endangered by hazardous voltages or currents transmitted through the connections made with the patient""s body.
The present invention solves these problems identified with prior art external instruments including programmers, analyzers and other equipment and accessories used to test or communicate with IMDs involving interface devices that enable expansion of the capabilities while minimizing the space required and maintaining or increasing patient safety.
In one aspect of the invention, the invention is compatible with remote patient management systems that interact with remote data and expert data centers. Specifically, the invention provides a data communication link that is able to transfer clinical data from the patient to a remote location for evaluation, analysis, storage in data repositories, and clinical evaluation without exposing the patient to electrical hazards. The data communication link is compatible with various data mining and network communication systems such as the Internet, intranet and the World Wide Web.
The data communication link comprises in one embodiment, a modem card adapted to be inserted into and removed from a programmer at a modem connection terminal and an isolator in the programmer coupled to the modem connector to block hazardous electrical signals passing through the modem from reaching a patient coupled with the programmer. The appropriate modem drivers and associated software are readily loaded onto the programmer operating system disk drive. The removable and replaceable modem and modem software enables selection of the optimum modem for use in any country or region of the world.
In a further aspect of the invention, the programmer is formed having an expansion bay extending into its case that is adapted to receive a series of interchangeable expansion modules to extend the capabilities of the programmer. Each such module is formed having a housing that fits into the expansion bay in the housing of the programmer. Each such module is formed with module connector terminals adapted to mate with programmer connector terminals of an expansion bay interface connector when the module housing is seated in the expansion bay. The modules generally can expand memory capacity or provide signals to or receive signals from the on-board operating system and are rendered operational with software loaded onto the operating system hard drive when the module is used.
In this aspect of the invention, any such module that is coupled with the external environment that could conduct hazardous electrical signals into the programmer or from the programmer to the patient includes internal isolation of the module operating system to block such hazardous signals conducted on data lines and an isolated power supply to supply power to the module operating system. Such modules that present patient hazards may be a PSA and/or DSA module or a temporary pacing module or a cardioversion/defibrillation module that is coupled to the patient through pacing and/or cardioversion/defibrillation leads, respectively, that are in direct contact with the patient""s heart. Or, the module may be a physiologic sensor module for sensing a physiologic parameter, e.g., blood pressure, temperature, pH, and gas concentrations, through an indwelling catheter or lead extending a sensor into the patient""s body.
In accordance with this aspect of the present invention, the modules are preferably formed having an internal isolation barrier that isolates the module connector terminals that mate with the programmer connector terminals from the module operating system. Moreover, the expansion module preferably includes a battery back-up power source that can power the module operating system in case the programmer power supply fails or even if the module is removed from the expansion bay. In the latter case, the internal isolation barrier prevents any hazardous electrical signals from being conducted from the module connector terminals to the module operating system and from there to the patient""s body.
In a variation of this aspect of the invention, the expansion bay interface connector terminals can also or alternatively be isolated within the programmer by an additional or alternate expansion bay signal interface comprising an opto-isolator and an isolated power supply.
In accordance with a still further aspect of the invention, testing of the IMD can be conducted while data is received from the IMD, and further data can be gathered from another IMD or auxiliary external medical devices employing a further analog signal input/output cable and box. For example, an IMD may be coupled to an expansion module for testing and recovery of data while the analog signal input/output cable and box are coupled with a physiologic sensor for sensing a physiologic parameter, e.g., blood pressure, temperature, pH, and gas concentrations, through an indwelling catheter or lead extending a sensor into the patient""s body.
In yet another aspect of the invention, analog signal carrying cables, e.g., ECG cables to ECG electrodes on the patient""s skin and analog signal cables extending to remote equipment, are adapted to be attached to cable connector terminals of the programmer. Such cables can conduct hazardous electrical signals into the programmer or from the programmer to the patient. The programmer includes optical isolators coupled with the cable connector terminals to block such hazardous signals.
Thus, the capabilities and flexibility of the instrument are magnified without unduly increasing size and weight, and safety systems are provided for protecting the patient from harm due to electrical potentials.
This summary of the invention the advantages and features thereof have been presented here simply to point out some of the ways that the invention overcomes difficulties presented in the prior art and to distinguish the invention from the prior art and is not intended to operate in any manner as a limitation on the interpretation of claims that are presented initially in the patent application and that are ultimately granted.